Piezoelectric fuse



Uflltfid States The invention described herein-may be-manufactured -and used by or for the Government for governmental purposes, without the payment'to'us'of any royaltythereon.

This invention relates to detonator' fuses for projectiles, and more 'particularly to a detonator-fuse actuated =re- 'motely from the point of impact of the projectile.

A=main object of this invention'is'to provide aidetonator fuse actuated remotely from-thepointiof impactof the :projectile wherein the time lag-between impact :of '-the1'forward ;.p ort-ion :of the projectile with Ethe target {and the detonation of the charge carried by thegprojectile {is reduced tea-minimum. 1 1

'-A further object-of thisinvention-isto provide a detonaftor fuse actuated by the-voltageg'enerated across thefaces 'of :a piezo-electric :eleme'nt resulting from :the stresses generated in the piezoelectric element due to impact of the projectile'with-itstarget. s Further objectsof this invention iWil-l appear from the following description and claims, and from the acconr panying drawings, wherein: H p

Figure 'lis "alongitudinal"crossg'sectiona'lview of the forward and rear-portionsof a projectile provided with a ipiezo-electricdetonator fuse accordingto thisiinvention. "Figure 2-isra detail view taken on line 2-2 of Figure 1.

In projectiles of the armor-piercing type, it is very desirable to detonate the charge while themain body portion of i thefprojectile'tis still a short distancein fr'ont of th'eithlget.

.This featureiis essential in order togpr'operly fdirect the trance of the explosion of the chargeiin-zsuch a m'anner as flto obtain the desired penetrating. effect 1 The above desired timing of detonation has heretofore been attempted by the employment of a mechanical triggering device located at the nose of the projectile connected to a base-mounted detonator by mechanical means, or by inertia-actuated means actuated by acceleration derived from impact. In the various mechanical methods which have been employed, the time required for detonation after contact of the nose of the projectile with the target has been substantial with respect to the time required for the projectile to lose its momentum after impact, and therefore the triggering action has not been altogether satisfactory in these methods for properly timing the detonation.

In the structure of this invention a piezo-electric element is employed as the triggering device, and inasmuch as the piezo-electric effect is practically inertia-less due to the fact that very small masses are involved in the production of the piezo-electric voltage, the triggering action can be made almost instantaneous by proper design of the triggering circuit.

Referring to the drawings, 6 designates a projectile of the armor-piercing type containing a main charge adapted to beexploded by a detonating charge 14, mounted in a housing 13 in the base of the projectile. Detonating charge 14 is adapted to be exploded by a spark at spark gap 24. Spark gap 24 is grounded at one contact and is connected at the other contact to a pivotally mounted armature 18. Armature 18 is biased to a position of conggering -circuit connected to spark .gap

tact with a contact point 26 by'a tension spring 25 con- 'nected' to an insulating sleeve 40 around armature 18 and to housing 13, but -is-- normally held inopen circuit position by a projection 16 on a rearwardly movable slide member 21. Spark gap24 is also normallyshort-circuited by the contact of projection-16 with armature- 18. When member 21 moves rearwardly upon firing, armature "-18 makes contact with contact point -26 whereby }the spark gap is connected by conductor 7, which extendsthrough an insulating sleeve 8, through-the body of-theiprojectile to piezo-electric trigger member 2.

Piezo-electric member-2 comprisesa pair of 45 cut Rochelle-salt crystalslabs mounted -so'that compression on the top-and bottom faces produce like chargesatthe .inner vertical facesof one polarity, andlike charges at the outer vertical faces of the other polarity. The inner vertical faces are in intimate contact with a common median electrode 23 and the outer vertical faces are provided with intimatelycontacting face electrodes 22.

The 'electrodesyma-y'be of-gold plating, silver plating or any 'other suitablemetallic material, ormay betsoli d metal electrodes.

. Themedian-electrode-234s connectedto conductor 7, "as shownin Fig. 2 andthe outer faceelectrodes 22 are v.grounded-tothe metal partition 4 forming part of the body of the projectile.

Nose 1 of the projectile is .provided with: an appropriate recess which receives -the-;top;portions of the crystal slabs -and-is secured so astoeli-minate-all longitudinal looseness of said slabs. Afreemargin is providedbetween medianelectrode 23 and the outer surfaces of t-hecrystal-slabsas shown in Figs 2, to prevent-the .crystals from beingshort-circuited. p I

Conductor 7 is madeas short as possible and-theelec- 1 trodes .-22 and 23 -may be likewise designed for minimum crystal shun t capacitance. The total crystal shunt capacitance should be -made as-smallas possibleain order t0- provide a voltage waveof-maximum steepness inthe trig- 24; This is nece s saryin order to minimize the time-lag betweenlimpact and detonation. -1

fIt Wl ll heapparentthat impact of nosel with the target, which is; instantaneously communicated to crystal member -2, will result in a substantial piezo-electric voltage being generated at electrodes 22 and23, which willbe a most instantly transferred (vi here the circuithas been properly designed for minimum shunt capacitance) to spark gap 24. The spark at gap 24 will explode detonating charge 14 causing the main charge to be set off.

For best results, the leakage resistance of the circuit must be high and the series resistance of the conductors must be low. Inductance should be also minimized to make the discharge as non-reactive as possible, so that maximum spark energy is dissipated in a very short period of time.

The mass of the nose 1 and the mass of the crystal element 2 are insufiicient to produce substantial distortion of the crystal element as a result of firing reaction, so that the voltage at spark gap 24 is insutficient to detonate the charge when the projectile is launched.

Although the foregoing embodiment of this invention discloses the piezo-electric element as actuated by direct impact of the nose of the projectile with the target, said piezo-electric element may, if desired, be actuated by an inertia element placed behind the piezo-electric element and adapted to deliver its momentum thereto when the projectile strikes its target. In this case, the piezo-electric element may be located at the base of the projectile adjacent the spark gap element. This arrangement introduces a slight time lag, which is required in order that the inertia element transfer its momentum to the piezoelectric element, but this is somewhat compensated for in that the electrical connections may be materially shorttric element mounted in pression of the piezo-electric element.

Safety in handling is provided by a safety pine 30 which normally extends through the projectile and engages a shoulder or slide member 21 to hold said slide member in forward positionwhereby the spark gap is short circuited and the energizing circuit therefor is open-circuited. When the projectile is ready to be fired, safety pin 30 is pulled out. The set-back caused by firing the projectile moves slide member 21 rearwardly and releases armature 18, thus preparing the energizing circuit for producing a spark across spark gap 24 when nose portion 1 strikes the target.

Although a specific embodiment of the invention has been disclosed in the foregoing description, it will be understood that various modifications within the spirit of the invention will occur to those skilled in the art. Therefore it is intended that no limitations be placed on the invention other than as defined by the scope of the appended claims.

What is claimed is: p

1. A detonator for a projectile comprising a piezo electric element, a detonating charge, means for setting off element, and means responsive to impact of said projectile for stressing said piezo-electric element.

2. A detonator for a projectile comprising a piezoelectric element, a detonating charge mounted in the base of the projectile, means for setting oif said charge responsive to stressing ofsaid piezo-electric element, and means responsive to impact of the forward portion of said projectile for stressing said piezo-electric element.

3. A detonator for a projectile comprising a piezo-eleca portion of the projectile, a detonating charge mounted in another portion of the projectile, means, for setting off said charge responsive to stressing of said piezo-electric element, and means responsive to impact of said projectile for stressing said piezo electric element whereby said charge is set ofi.

4. A detonator for a projectile comprising a piezo-electric element mounted in a forward portion of the projectile, a detonating charge mounted in a rear portion of the projectile, means for setting off said charge responsive to stressing of said piezo-electric element, and means responsive to impact of the forward portion of said projectile for stressing said piezo-electric element whereby said charge is set mi.

5. A detonator for ajprojectile comprising a piezosaid charge responsive to stressing of said piezo-electric electric element mounted in the projectile, a detonating charge also mounted in the projectile, means for stressing said piezo-electric element responsive to impact of the projectile, spark gap means in the detonating charge, said piezo-electric element being electrically connected to said spark gap means and being adapted to produce a spark across the gap to set off the detonating charge when the piezo-electric element is stressed by impact of the projectile. .v

6. A detonator for a projectile comprising a piezoelectric element mounted in the projectile, means for stressing said piezo-electric element responsive to impact of said projectile, a detonating charge located in the rear portion of said projectile, a spark gap positioned in said detonating charge, means electrically connected to said piezo-electric element and said spark gap for producing a spark across the gap when the piezoelectric element is stressed whereby to set off the detonating charge.

7. A detonator for a projectile comprising a piezoelectric element mounted in the forward portion of the projectile, means in the forward portion of the projectile for stressing the piezo-electric element responsive to impact of the forward portion of the projectile with a target, a detonating charge located in the rear portion of the projectile, a spark gap positioned in said detonating charge, means electrically connected to said piezo-electric element and saidspark gap for producing a spark across the gap when the piezo-electric element is stressed whereby to set otf the detonating charge.

8. The structure of claim 7 and wherein the means for stressing the piezo-electric element comprises a nose mem ber secured'to the projectile against which the forward portion of the piezo-electrie element is positioned and a supporting memberpositioned against the rearward portion of the piezo-electric element, said supporting member being rigidly secured to he body portion of the projectile.

References Cited in thefile of this patent V UNITED STATES PATENTS 384,662 Zalinski June 19, 1888 1,791,606 Ruhlemann a Feb. 10, 1931 t FOREIGN PATENTS 773,866 France Sept. 10, 1934 149,723 Austria L. May 25, 1937 91,592 Sweden Feb. 24, 1938 549,998 Great Britain Dec. 17, 1942 

